History:
Elves, or Elfball as it used to be called, was born as an odd Conley Woods-style concoction in Time Spiral – Lorwyn era Standard. (https://www.youtube.com/watch?v=d6esx8XyD2I) The deck played a bunch of small critters that made a lot of mana enabling the pilot to play a lot more small critters, then fill his hand with Distant Melody, do it again and do it again. At some point, a Roar of the Crowd counted the Elves and shot the opponent into the face for a small amount of damage. It was a janky deck, raw, but with lots of potential.

That potential was fulfilled in 2008, in the Extended format, where everyone ever was playing Elves. The larger card pool allowed people to play better and cheaper Elves and eschew the expensive draw engine of Distant Melody in favour of Glimpse of Nature. The deck took the tournament by storm – 6 decks in Top 8 were Elves (https://www.wizards.com/magic/magazine/article.aspx?x=mtg/daily/eventcoverage/ptber08/t8decks), an Extended combo mirror went to time on game one with a 116/116 Predator Dragon on the board that no one cared about because the players’ life totals had four digits and there were 200 or something Insect tokens on the board. Ultimately, Luis Scott-Vargas’ streamlined Grapeshot build won the day – optimized to be the faster deck in the mirror, unsurprisingly.

After PT Berlin, Elves abandoned the Predator Dragon kill, opting for Mirror Entity and occasionally Grapeshot or both. It stayed on the radar in Extended and Legacy for a while, but was rarely something truly big – it was a nice deck, but always felt like it was in search for something. Green Sun’s Zenith supplanted and complemented other tutoring options, giving the deck a better fair gameplan.

Countertop Miracles became a deck, and it was game over for Elves, if not for Return to Ravnica.

Return to Ravnica saw the printings of Deathrite Shaman and Abrupt Decay, two cards which dramatically impacted Legacy in many ways. For Elves, these cards meant built-in reach, easier splashes for colour, some game against graveyard decks which they struggle against, and a way to kill Counterbalance. With the need for black, a standard fetch-dual manabase was adopted. This enabled Cabal Therapy from the sideboard to combat fast combo decks, something Elves is historically absolutely horrible against.

Simultaneously it was discovered that Natural Order for Craterhoof Behemoth is kind of broken, and often a quick kill with barely any setup. This got rid of the waiting time disadvantage Progenitus had in many matchups. Thus GBw NO Elves was born, with usual suspects Luis Scott-Vargas and Matt Nass piloting the new build to high finishes in Grand Prix Denver (http://www.mtgthesource.com/forums/showthread.php?17168-Deck-Elves-Combo&p=695673&viewfull=1#post695673). Much improved over the deck’s previous iterations, it has become a strong presence in the pre-Theros Legacy metagame. This new version can’t properly be called a budget deck anymore, but the basic gameplan is modular in many ways and budgetizes surprisingly well in comparison to most common suspects without being a T1 glass cannon deck that doesn’t really even play Magic.

The sideboards vary a lot based on players’ card availability and taste, but the maindeck is relatively tight. In my mind, the questions you have to answer when building a maindeck:
1. What is your second Natural Order target? One Craterhoof is a must, but the second one can vary wildly. I personally prefer a Regal Force or Ruric Thar, the Unbowed, but a second Craterhoof has a lot of merit.
2. Utility creatures? I settled on Viridan Shaman, Scavenging Ooze and Elvish Archdruid. Of these the third is unconventional and others would prefer playing something else in the slot, even a land or a third NO target.
3. How many Cradles and Crop Rotations? For me, a 2/2 split feels right, but 3/1, 4/0 and 4/1 or 3/2 (shaving a card elsewhere) are all valid options. If you’re on a budget and can’t afford Cradles, multiple Priests of Titania and Archdruids are one good way to go, but skew card valuation a LOT. Do not draw conclusions of a card’s value in NO lists from playing a Priest list, and the reverse.

Gameplan, or Why play the deck:
Elves is an interesting deck in many ways. On one hand, it is a fast combo deck capable of killing the opponent at the drop of a hat with tons of tramply damage or obscene amounts of mana and card draw into the aforementioned tons of tramply damage.

On the other hand, Elves is a slow, grindy aggro deck with lots of interesting synergies that can be used to gain an advantage over a long, drawn-out match. That many Legacy decks lack proper card draw, opting for 2-for-1’s and cantrips instead leaves Elves in a good position. Who wouldn’t want a repeatable draw engine? It’s also never been said that Glimpse of Nature would have to kill someone. Last I checked, Ancestral Recall is a pretty ok card and we just happen to play it.

The rosy side is a deck able to play a completely degenerate combo game with the best of them, and a deck able to grind it out with the best of them. The thorns come from the tools used to accomplish that: Your deck is purely positive: You build your own resources, but few cards in your maindeck do anything to hinder your opponent’s development – the usual answer is just going bigger. The second downside is that you’re playing a deck full of just about the most hateable kind of permanent in the game: Small creatures that all share a colour and a creature type and rely on synergy with other similar cards to be worth anything. Still, those small creatures do win.

Key interactions:
Elves, as a deck, doesn’t have a single key card without which the deck is crippled – the multiple gameplans hedge against that. Each game plan, however, has it’s own needs.

Elves was once primarily a combo deck, but the last two versions – both the Gw Mirror Entity one, and the new GBw NO list, are primarily grindy aggro decks with the extra potential to just kill the opponent.

With that in mind, the beating heart of the grinding gameplan is without a doubt Wirewood Symbiote.
With Elvish Visionary, it is a repeatable draw engine and fog effect that allows you to bury the opponent in card advantage.
With Viridian Shaman, you have repeatable artefact destruction to give Affinity and Stoneforge decks hell. With both Wirewood Symbiote + elf and Quirion Ranger + Dryad Arbor, you can have a makeshift Maze of Ith to prevent Jitte from gaining counters, the Mirrodin Swords from triggering, Batterskull gaining life and the like. Or you can just prevent some damage and score an additional card draw for your trouble.
Quirion Ranger and Wirewood Symbiote are able to repeatedly untap Deathrite Shamans, which gives the deck a surprising amount of reach and ability to win Deathrite wars.

The broken combo side of the deck is defined by Nettle Sentinel’s interactions with Heritage Druid and Birchlore Rangers. With two Nettles and a Heritage Druid in play, any 1-mana creature is a green Dark Ritual.
With an active Glimpse of Nature, that Dark Ritual draws you a card. The Symbiote-Visionary interaction can easily gain you three cards and three mana. The combo engine can quickly amass lethal board states and insane amounts of mana and be left with a full grip of cards.
Sometimes, a lone Craterhoof swinging without any friends can deal hilarious amounts of damage. That Craterhoof can easily be lethal all by itself. If you run a Priest of Titania or an Elvish Archdruid, twiddling those can obviously result in all manner of absurdity.

Sideboard plans:
Elves is an engine deck, and as such sideboarding has to be careful and usually very minimal to avoid diluting the deck’s core strength. If you have much less than 30 creatures, Glimpse will start failing randomly, for example, and you just won’t draw enough critters to form any kinds of powerful synergies, let alone the right ones.

The exception to this is dedicated combo decks. Against decks such as Storm, Show and Tell and Reanimator, that philosophy has to be abandoned. They pack more disruption maindeck than you do, in Reanimator’s and Storm’s case are faster to go off than you, and their speed is impacted less by playing disruption than yours is. This means the main reasonable strategy is to cut heavily into the numbers of Elvish Visionary and/or Glimpse of Nature, board in a heavy disruption suite and play an aggro-control type of strategy of simultaneous disruption and beatdown and hoping to get there in time. Some powerful hate permanents can win the game for you by itself, especially against Storm, but it is not something you should count on.